1. Field of the Invention
This invention relates to an anti-embolic filter for the prevention of blood emboli, and more particularly a vena-cava filter against cruor embolism.
The main purpose of the filter is to arrest the migration of thrombi coming from peripheral venous flow of the inferior limbs or lower pelvis and circulating in the direction of the pulmonary arteries, where the thrombi could cause severe and often lethal emboli by obstructing the large branches.
2. Description of the Prior Art
Various inferior-vena-cava filters have been developed and are described in the article by J. DRILLER et al., entitled "New percutaneous caval filter device for pulmonary thromboembolism", in Medical and Biological Engineering, November 1976, New York, pages 629 to 635.
Such a filter generally has an expansible body which is collapsible into a generally cylindrical form so as to introduce it in a catheter and to push it in the latter to the place of implantation of the filter in the inferior-vena-cava. When the body of the filter leaves the catheter, it then spreads out in a revolution form in the vein thereby enlarging the cross-section of the vein and obstructing all dangerous foreign bodies, such as blood clots, liable to cause a pulmonary embolism.
MOBIN-UDDIN holed umbrella disclosed in U.S. Pat. No. 3,540,431 is an endovenous filter which requires surgical access of the internal jugular vein under local anesthesia. The MOBIN-UDDIN filter has several inconveniences. To insert the umbrella filter, it must be folded and screwed into a tubular capsule of an adapter which is pushed by means of a flexible tubular catheter to the place of implantation. The adapter is bulky and does not enable the filter to be introduced through narrow and tortuous jugular veins. Furthermore, the umbrella filter is liable to migrate some distance or to topple. The filter often entails thrombosis, sooner or later, causing an inferior venous stasis syndrome
The more recent Lazar J. GREENFIELD filter is comprised of an assembly of stainless steel undulated wires which are connected together by means of a metal capsule and which are unfurled according to conic generating lines, like the struts of an umbrella. The inconveniences of this filter are analogous to those of the MOBIN-UDDIN filter. However, the GREENFIELD filter can be introduced via the femoral vein or the jugular vein, by means of a very high sized introducer of type 24F, having a diameter of 7,92 mm. This filter requires a surgical denudation or a percutaneous access. The plurality of radial filter anchoring hooks due to the sharp and curved free extremities of the wires appears to be traumatic for the venous wall. The malpositions of the filter in the vena cava and the migration of the filter to the heart are not exceptional.
A third endovenous filter, known as the GUNTHER filter, is comprised of a first tubular flexible envelop (basket) comprised of predeformed axially twisted metal wires, and of a set of curved wires attached at one extremity of the envelop and analogous to a GREENFIELD filter. When the filter is unfurled, the envelop has a longitudinal section substantially delimited by two opposite sinusoidal alternations. The radially compressed envelop of the GUNTHER filter has still a relatively large diameter requiring the use of a large introducer catheter of the 10F type, corresponding to a diameter in the order of 3.3 mm.
All these known filters also necessitate complex equipment that is specially designed to introduce the filter into a particular catheter of great size 9F to 24F. Indeed, the filter must be pulled into a sheath, also called as an adapter or cartridge, by means of a hook so as to reduce its cross-section to the internal cross-section of the catheter, then the sheath is plugged into a proximal extremity of the catheter, so as to push the filter in the catheter. With all known filters, their reduced cross section in the catheter depends on the great number of wires bunched together, which restricts the use of these filters to veins of relatively large diameter, or at least, increases the duration and the difficulties of the surgical operation.